96 THE VICTORIAN NATURALIST. 



paces. The lamp was simply a culture of photogenic bacteria 

 in a large glass flask, and as there is no heat about such an 

 arrangement, it is suggested that it would be useful in powder 

 magazines or in dangerous mines. 



The most brilliant and most varied and interesting cases of 

 phosphorescence are to be found among animals, and there 

 seems hardly one of the larger groups which does not furnish 

 some instances of it. We find animals, large or small, highly 

 organized or simple, living on land or in water, apparently 

 irrespective of relation in any other way, all resembling one 

 another in the power of glowing in the dark. All the members 

 of the same group of animals are not necessarily phos- 

 phorescent — indeed, this property seems to occur so irregularly 

 in Nature that Darwin (ii, p. 150) mentions luminous organs 

 as being one of the "special difficulties of the theory of natural 

 selection." " When the same organ is found in several members 

 of the same class," he says, " especially if in members having very 

 different habits of life, we may generally attribute its presence to 

 inheritance from a common ancestor .... but this is far 

 from the case here." This sentence was written about the electric 

 organs of fish, but later he says : — "The luminous organs which 

 occur in a few insects belonging to widely different families, and 

 which are situated in different parts of the body, offer, under 

 our present state of ignorance, a difficulty almost exactly parallel 

 with that of electric organs." 



As, then, phosphorescence occurs so widely, it would be 

 impossible for me even to name all the animals which have this 

 property, so I shall divide them into land and marine forms and 

 try to touch on a few interesting types of each. 



In the case of land animals, it seems to be among the smaller 

 ones, such as earthworms and insects, that luminescence, except 

 that caused by bacteria, is noticed. 



Amongst the Oiigochaeta, or earthworms, several luminous 

 species have been observed, the most noteworthy in Europe 

 being Photodrilus 2)hosphoreus, a small worm recorded by Giard 

 in 1887. Giard says that the luminescence proceeds from 

 glandular organs in the anterior part of the body. The large 

 white New Zealand earthworm, Octochcetus multiporus, was 

 found by Professor Benham, of Dunedin, to discharge in the 

 dark a brilliantly phosphorescent fluid from the dorsal pores. 

 Another luminous earthworm may often be seen at night on 

 garden paths round our suburbs, especially after rain. It is 

 whitish in colour and about ly^ in. long. As well as glowing 

 itself, it leaves often a phosphorescent track, which is most 

 deceptive when one is trying to secure them. 



Centipedes are very commonly seen to be phosphorescent in 

 England, usually in the summer. In this case defence seems to 



